Behavioral and pharmacological specificity of the feeding elicited by cholinergic stimulation of the substantia nigra in the rat

Microinjections of the cholinergic agonist carbachol into anterior substantia nigra dose dependently increased food intake in satiated rats. This resulted from a prolongation of the duration of eating. In the absence of food, those doses of carbachol that stimulated food intake (.1 and .5 μg) had no effect on any other response examined, including gnawing, drinking, locomotion, grooming, sniffing, and rearing. The effect of carbachol depended on the degree of prior food deprivation, but supra-additive effects of carbachol and deprivation were not observed. These results are contrasted with those of previous studies demonstrating the nonspecific behavioral effects of electrical stimulation of the brain and of studies showing that carbachol has radically different behavioral effects at other central nervous system sites. Microinjection of an acetylcholine/eserine sulfate mixture also significantly increased food intake. This response was abolished by prior microinjection of the muscarinic receptor antagonist atropine into the substantia nigra, a result that provides evidence for pharmacological specificity of the behavioral effects. These data provide further evidence for the hypothesis that a functional cholinergic system is present within substantia nigra.